STAR STRANGENESS! K0sK0s K+K+ (Preliminary)
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Transcript of STAR STRANGENESS! K0sK0s K+K+ (Preliminary)
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STAR STRANGENESS!
K0s
K+
(Preliminary)
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What do we measure?
K+ (us) 494MeV ++ccm
K0s (ds) 498MeV ++ ccm
uds) 1116MeV p+- ccm
(dss) 1321MeV +- ccm
(sss) 1672MeV +K- ccm
0 (ss) 1020MeV K++K+ ccm
+ anti-particles + other more exotic resonances ((1520)!)
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What do we measure (2)?
Particle yields
How much is created?
Spectra (dN/dy, dN/dpt, d2N/dydpt)
Where and when are they created and what are the dynamics?
Particle ratios
What are the chemical potentials?
Interferometry
How large is the source and how long did it exist?
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Tfireball < Tc Hadron gas
Hard to make S 0 particles
+ N + K (Ethresh 530MeV) + K + (Ethresh 1420MeV)
Mtm phase space suppressedNeed to create 3 qq pairs
(initially there are no q) with similar momenta in a region already containing many quarks.
Why are we interested in Strangeness production?
Tfireball >Tc QGP
Easy to make s quarks E=2ms ( 300MeV)Free gluons
g-g fusion - dominate s s creation faster reaction time than qq
Pauli blocking may aid creation of s s quarks
( probably not true at high T, too many states).
¯
¯¯
¯
¯
¯
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What is the best thing to measure?
While K’s carry ~70% of the strangeness they are easily produced in the final stage reactions as the hadrons in the expanding gas interact and
already show an enhancement over N-N collisions at energies too low
to form a QGP.
Want to look at the yields of multi-strange (anti-)baryons
production suppressed in Hadron Gas because
a) need large energy to create
b) need to create u d s where there are already many ud
c) need to create them in the same mtm phase space
Looking at the particle ratios ptells you the s/u ratio -> 1 if there is chemical equilibration
¯
¯¯¯
¯ ¯ ¯¯
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Evidence for Strangeness Enhancement - WA97 results
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Strange particle ratios
AGS > 1 and is higher than SPS.
Seems to be a clear strangeness enhancement between pA and AA
collisions at the SPS
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Where are the strange particles produced?
If heavy ion collisions were just N-N reaction superpositions
(uds) concentrated in the baryon rich projectile regions
(uds), K0s(ds) peaked at mid-rapidity
due to their sea-quark content
PROBLEM!
What if there is any stopping?
Baryon-rich projectile and baryon-free
“fire-ball” region become merged
Have to separate fire-ball creation from that merely due to associated production
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Stopping and the net distribution
We expect that the net
yield should follow the net p yield.
However there is a distinct “bump” about mid-rapidity in the
distribution that is not observed in the p.
Is this NEW physics?
Or is it evidence of feed-down into the channel that has yet to be corrected properly. NA49 have
recently obtained and results
which may help answer this question
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Freeze out “Temperature” vs Mass
From two particle correlation studies you can extract 2/T from R.
~50% transverse kinetic energy goes into radial flow.
-> Very important for any global thermo-chemical analysis
Tprop = 120 ±10MeV
= 0.5
N.B
(Na49) T=305 MeV
(Na50) T=213 MeV
Also 3x smaller yield
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K+/- +/- +
K+, K- High Pt identification via “Kink”Analysis
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Finding V0s
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STAR TPC Acceptance for B=0.25T (Half Field)
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—
The peaks in their glory
332K Events |z|<50cm, |y|=0.5, GeV/c
0.16/event 0.13/event
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154K MinBias Events |z|<50cm, |y|=0.5, GeV/c
And there’s more
0.0009/event0.2/event
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STAR STRANGENESS!
K0s
K+
(Preliminary)
![Page 19: STAR STRANGENESS! K0sK0s K+K+ (Preliminary)](https://reader036.fdocuments.us/reader036/viewer/2022062516/56649d535503460f94a2f093/html5/thumbnails/19.jpg)
In case you thought it was easy…
Before
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And Voila!!!!
After
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• Large peaks at 2 o’clock and 8 o’clock
• TPC pad row “floating”
Fine way to calibrate a detector..
Now in ExB “Hell”
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• Baryons distributions carry information related to– stopping and particle production– baryon chemical potential– thermal equilibrium
• p/p ratio should be sensitive•
• Last call for RHIC predictions (nucl-th/9907090) at sNN = 200 GeV :– Quark Coalescence: p/p = 0.6– Fireball: p/p = 0.9 - 1.0– Hijing: p/p = 0.8– RQMD: p/p = 0.5
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p/p: centrality and pt dependence
• No strong pt dependence• Weak centrality dependence
more stopping and/or other process ?
85% centrality 6% Ratio for 0.3 < |y| < 0.4
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/ preliminary
= 4 MeV
332K min bias Events0 < pt < 2.3 GeV/c0.5<y<0.5
¯
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p/p
@AGS
@SPS
p/ p E866
+
+
p/ p NA49
WA97
p/ p STAR
STAR-
---
-
AGS SPS RHIC
STAR Preliminary
/
ratio
Anti-Baryon/Baryon Ratio
Preliminary: / = 0.70 0.05 (stat) 0.2 (syst)
p/p = 0.65 0.03 (stat.) 0.06 (sys.) ¯
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Conclusion
Stay tuned for QM2001!!!!